Framing Roof Vapor Barrier

The history of cold climate vapor barriers itself is a story based more on personalities than physics.

Framing roof vapor barrier.

Hvac units roof materials etc loads to the supporting joists or purlins. A vapor barrier under your concrete slab is essential for moisture prevention. We ll add a vapor barrier so the moist air does not flow up through the insulation and condense on the roof. A vapor barrier under your slab will also protect you from harmful ground pollutants like radon gas.

Crawl spaces benefit from a polyethylene moisture barrier placed directly over the exposed earth. It is frightening indeed that construction practices can be so dramatically. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. The two main types of substrates used with metal roofing systems are open framing and solid substrates composite or plywood.

Understand these are climate specific recommendations. Vapor barriers are a recommendation but not a requirement by a number of roofing panel system manufacturers. That reduction of air and moisture infiltration can then help improve roof longevity. A vapor barrier against the concrete surface is generally recommended before wood framing or flooring materials are installed.

Vapor barriers are also a cold climate artifact that have diffused into other climates more from ignorance than need. Add a preinstalled membrane to absorb and release the condensation as it forms with the natural weather cycle traditionally we ve insulated the roof panel to try and keep the temperature on the panel from reaching the dew point. It serves as a structural member transferring the weight of both live ex. Class i vapor retarders i e.

To know if you need a vapor retarder ask yourself a few basic questions. A roof design that includes an adhered roof membrane with multiple layers of insulation with board joints offset and staggered over a vapor retarder air barrier helps lower the risk that air and the moisture it carries will infiltrate the roof system. Vapor barriers can be installed in vented roof assemblies in climate zone 6 and climate zone 7 but should be avoided in climate zone 5 as top side condensation may occur in the summer months during air conditioning periods. Rose 1997 regales readers of this history.

Some moisture load in conditioned post frame buildings can be relieved via diffusion hence a vapor retarder in a ceiling rather than a vapor barrier through a roof assembly able to handle it example a vented attic in a moderately cold climate or mixed climate. In theory if a building houses a moisture producing activity such as a kitchen or locker rooms then a vapor barrier is essential to slow moisture from escaping into the roofing system. That air condenses on the cooler concrete floor.